1. Technical Field
The technical field relates to a backlight apparatus and liquid crystal display apparatus, and more particularly to an LED (light emitting diode) backlight apparatus in which a plurality of LEDs are placed and a liquid crystal display apparatus having this.
2. Description of the Related Art
There is one kind of liquid crystal display apparatus that illuminates a liquid crystal panel using an LED backlight apparatus (hereinafter referred to simply as “LED backlight”).
Unexamined Japanese Patent Publication No. 2007-165632 describes an example of a conventional liquid crystal display apparatus that has an LED backlight. In this liquid crystal display apparatus, control is performed to increase the brightness of some of the LEDs provided in the backlight—for example LEDs placed in an area in which the ambient temperature is high, such as those close to a circuit with a large calorific value—by increasing the amount of drive current or the period for which that current is applied. Backlight brightness is made uniform by means of this control.
However, a property of an LED is that the higher its ambient temperature, the faster is the aging degradation of its brightness and the shorter is its life. Also, increasing the brightness of an LED by increasing its drive current amount or the like is a cause of aging degradation of LED brightness and shortened LED life.
Therefore, when control is performed to increase the drive current amount for LEDs placed in an area in which the ambient temperature is high, as in the case of an above-described conventional liquid crystal display apparatus, the aging degradation of those LEDs is more rapid than that of other LEDs. Consequently, as the cumulative illumination time of those LEDs increases, the brightness of those LEDs becomes lower than that of other LEDs. Therefore, uniformity of backlight brightness cannot be maintained over a long period. In other words, even if uniformity of brightness is maintained in the initial state, that balance is lost after a long period of use.
Also, even if the amount of drive current or the like is increased for LEDs whose brightness decreases to prevent a decrease in the brightness of those LEDs, there is a limit to the increase in the drive current amount, and a situation will eventually arise in which uniformity of brightness cannot be maintained.